The present invention relates to an irrigation sprinkler control system wherein a clock timer controls the duration and time of day for watering. A combination switch consisting of a series connected humidistat and a cooling thermostat compares the ambient humidity and temperature to preset threshold set points and is connected serially between the timer and the solenoid operated valves to prevent irrigation during and sometimes before inappropriate irrigation conditions exist.
Supplemental irrigation is needed in many arid areas for supplying water to the landscape shrubbery and vegetation. Clock 2 shown in FIG. 1, in conjunction with electrically activated valves 8 which supply water to the irrigation system, are often used to minimize the manual labor of such irrigation and to avoid loss of plants when irrigation needs are overlooked. The clock can be programmed to sequentially activate the solenoid valves 10 on a daily, weekly, monthly and yearly schedule for individual watering durations for each solenoid valve control. Such clocks often have a plurality of zones 23 which can be connected to different water control valves for the control thereof. Water is therefore delivered to each zone only in accordance with the programmed schedule. Maclay, Sanner and Coward have given some recognition in the art that it is thoughtless to operate the sprinkler system when it is raining, snowing or freezing outside. Many controllers have a manually controlled xe2x80x9crain switchxe2x80x9d which disables irrigation. If the switch is left off, no irrigation will be resumed when the rain stops and watering is again needed unless the switch is turned on again.
Other controllers 2 have a series connection to which a rain xe2x80x9csensorxe2x80x9d can be operably connected. The typical rain sensor is a water container with a float which operates a switch when sufficient rain water is collected. A more exotic variation of the above is the use of underground moisture sensing probes which are placed close to the timer controller. This prior art presupposes that the moisture level at the probe location is typical of the entire area to be irrigated. This led to the development of individual moisture sensors and probes that had to be located near the various greenery.
Still another more sophisticated approach is the use of a computer system into which historical-seasonal weather data such as evapotranspiration rates, relative humidity, winds, temperature etc. are programmed into the computer data bank so that a watering schedule may be predicted. This system offers a remote control link either via RF waves or direct signal interfaces with control valves but often lacks the capability to override the predicted schedule in the event of inappropriate watering conditions on a real time bases.
The object and advantage of this invention is to provide a real time-sprinkler control system upgrade which is weather and evapotranspiration sensitive to prevent activation of the sprinkler system when precipitation, temperature or E/T threshold levels are exceeded.
It is a further object and advantage of this invention to provide a weather and E/T responsive sprinkler control system upgrade which can be connected to a sprinkler control clock or a computer controlled link or other loads so that the clock or computer provides time control of sprinkler activation while a combination differential RH and temperature responsive sensor prevents activation of the sprinkler or other loads when the precipitation threshold is exceeded or the temperature is near freezing. The precipitation threshold has been discovered imperically to be the highest average relative humidity recorded by the National Weather Bureau for a given geographical area and at specific times of the day. The preferred embodiment has the following advantages:
a) it is inexpensive
b) it is simple to construct and is made up of standard components
c) it requires no power to function
d) it requires no software
e) it can sense unfavorable watering conditions before they exist.
f) it requires no probes
g) a single unit irrigation control can be linked to many irrigation controllers or loads.
h) it can combine evapotranspiration (E/T) sensitivity with RH when mounted near greenery.